Rotating Loosening Mechanism of a Nut Connecting a Rotary Disk Under Rotating-Bending Force

Abstract

Structures composed of a rotary disk and a shaft, which are fastened with bolts and nuts having tapered bearing surfaces, are loaded with a rotating-bending force. Upon investigation, two rotating mechanisms of the nut were derived. In one mechanism a high-pressure contact area is formed at the nearest loading point on threads and bearing surfaces. This leads to a difference in the curvature radii between the bearing surface of the disk and that of the nut. During the revolution of the disk, two friction torques occur in opposite directions on the bearing surface and the threads, respectively. The relative rotating direction of the nut is dominated by the greater torque. The other mechanism is due to the eccentricities caused by dimensional errors of the bolt, nut, and disk. By combining the two mechanisms, the rotations of the nuts either cause a loosening or tightening after many revolutions of the disk.

Study on self-loosening of bolted joints excited by dynamic axial load

“…This is one of the reasons why bolts, not nuts, are usually prone to fatigue fracture. The theoretical relationships between the tightening/loosening torques and preload are wellknown and given as [65,68] :…”

Self-Loosening Failure Analysis of Bolt Joints under Vibration considering the Tightening Process

“…The results showed that a small degree of loosening occurs when transverse load reaches the range 50 to 60% of the critical loading for the bearing-surface slip. Recently, the cycle rotation load has been accepted as another reason to cause self-loosening [10,11]. The results by Yokoyama et al [10] revealed that loosening occurs only when the rotation angle around bolt axis which is applied to clamped component reaches a critical value, and the thread surface undergoes a complete slip.…”

Variation of Bolt Loads of Axle Braking Disc under Continuous Braking Condition

“…。高速 列车运行过程中，由于轮对磨损不均匀，车轮会呈 现出多边形的状态。这种多边形的轮对在钢轨上滚 动时会出现强烈的振动激扰，这种振动传递到轮轴 系统中的关键部件，使得这些部件及联接紧固结构 的可靠性承受严峻考验 [5] 。交变载荷的另一个来源 是制动时产生的热应力。由于螺栓连接通常是在室 温下完成组装，热载荷必然会造成螺栓载荷的演化 和交变 [6][7] 。制动盘在制动过程中，巨大的制动热负 荷使制动盘结构中产生很大的温度梯度，但由于受 制动盘的结构约束，制动盘内部包括螺栓连接会产 生热应力 [8][9][10][11] 。 断口照片(图 1b)进一步显示疲劳裂纹从裂纹源 开始沿与螺栓轴向成一定倾斜角的平面扩展。这表 明该裂纹为 I 型和 II 型的混合型裂纹，即该裂纹在 远场拉伸应力和剪切应力(由横力弯曲载荷导致)共 同作用下发生疲劳扩展。弯曲载荷的出现对于螺栓 来说是灾难性的。通常的螺栓强度校核规范中只考 虑螺栓的拉伸失效，对于螺栓的拉伸疲劳强度也有 相应的测试标准 [12][13] 。对于螺栓弯曲疲劳强度由于 缺乏通用的实验测试标准，螺栓抗弯曲疲劳的数据 比较缺乏 [14] 。由于制造工艺的限制，螺栓会不可避 免的存在制造缺陷，在长期的交变载荷的作用下， 这些薄弱部位可能会产生微裂纹并扩展，造成螺栓 的最终失效。但现阶段，国内外针对列车制动盘螺 栓失效的研究还比较少 [15][16] …”